II.2. SQUASHES, PUMPKINS, ZUCCHINIS, GOURDS (CURCURBITA SPECIES) – 89
employed in North America as a float for fish nets, and this use may have facilitated
spread of the species in North America.
Cucurbita maxima
Taxonomically, the species C. maxima is composed of two subspecies, maxima and
andreana. C. maxima ssp. maxima contains ornamental and cultivated forms, while
C. maxima ssp. andreana contains only the wild forms. Gene sequence analysis work by
Sanjur et al. (2002) on the mitochondrial nad1 gene detects no base pair differences in an
intron of the mitochondrial nad1 gene between C. maxima and C. andreana, supporting
the assignment based on ecological and morphological evidence that these two species
form a wild/domesticated species pair (Nee, 1990). The work of Sanjur et al. (2002) also
shows that C. maxima is closely related to the free-living South American species,
C. ecuadorensis. This supports research using chloroplast DNA analysis which shows
that Cucurbita ecuadorensis groups with C. maxima and C. andreana to form a
South American group of allied species (Wilson, Doebley and Duvall, 1992). Nee (1990)
suggests that C. andreana appears to be ancestral to C. maxima, while Wilson, Doebley
and Duvall (1992) suggest that C. ecuadorensis, C. maxima and C. andreana are derived
from the same ancestor. Cucurbita ecuadorensis itself has been regarded as a species
subjected to an incipient domestication process which, however, did not continue (Nee,
1990; Sanjur et al., 2002).
Cucurbita moschata
Although a very important vegetable crop in many parts of the world (e.g. Africa),
C. moschata has been subject to less scientific scrutiny aimed at elucidating taxonomic
relationships within the species than C. argyrosperma or C. pepo. Filov in 1966 classified
more than 20 varieties of C. moschata into geographical subspecies. This classification
reflects several centres of diversity of C. moschata such as Columbia, Japan, Mexico,
Central America, the western United States, Florida, India and Asia Minor. Gwanama,
Labuschagne and Botha (2000), using random amplified polymorphic DNA analysis,
elucidated the relationship between 31 landrace genotypes obtained from Malawi and
Zambia. That analysis revealed four clusters, with genotypes from Malawi mainly
grouping in three clusters, while all genotypes from Zambia and three from Malawi
clustered in another group.
That C. moschata has a closer affinity to the Argyrosperma group taxa than to other
Cucurbita species has been argued from floral, seed and ecological similarities, and the
fact that these species are partially interfertile (Merrick, 1995, 1990). Sanjur et al. (2002)
confirmed this relationship through mitochondrial nad1 gene sequence analysis.
Cucurbita ficifolia
C. ficifolia has been subject to less scientific scrutiny aimed at elucidating taxonomic
relationships within the species than other cultivated Cucurbita. The species is
reproductively incompatible with the other species of the genus and shows far less
variability than the other species of the genus. The scant morphological variation of this
species is consistent with the limited variability in the pattern of isozymes studies
conducted so far (Andres, 1990). It has no associated wild ancestor in studies to date
(e.g. Sanjur et al., 2002).
Work by Sajur et al. (2002) examining a sequence of an intron region from the
mitochondrial gene nad1, and work by Wilson, Doebley and Duvall (1992) using
chloroplast restriction fragment length polymorphism, suggest that C. ficifolia is basal to